Selumetinib (INN),[13] sold under the brand name Koselugo, is a medication for the treatment of children, two years of age and older, with neurofibromatosis type I (NF-1), a genetic disorder of the nervous system causing tumors to grow on nerves.

[14] It is characterized by changes in skin coloring (pigmentation), neurologic and skeletal impairments and risk for development of benign and malignant tumors throughout life.

[14] Selumetinib can also cause serious side effects including heart failure (manifested as ejection fraction decrease, or when the muscle of the left ventricle of the heart is not pumping as well as normal) and eye toxicity (acute and chronic damage to the eye) including retinal vein occlusion, retinal pigment epithelial detachment and impaired vision.

[14] The approval was based on a clinical trial[23] of children who had NF-1 and inoperable plexiform neurofibromas (defined as a PN that could not be completely removed without risk for substantial morbidity to the child), conducted by the National Cancer Institute.

[14][22] The efficacy results were from 50 of the children who received the recommended dose and had routine evaluations of changes in tumor size and tumor-related morbidities during the trial.

[25] A Phase II clinical trial about selumetinib in NSCLC was completed in September 2011;[26] one about cancers with BRAF mutations is ongoing as of June 2012[update].

[27] In July 2015, selumetinib failed a Phase III trial testing whether the drug significantly prolonged the survival of patients in a study on melanoma originating in the eye.

[31] The combination of selumetinib to chemotherapy improved median progression-free survival in a trial of 510 patients with advanced KRAS-mutant NSCLC just for one month, which was statistically not significant.

[32] In November 2018, investigators working with nasal polyp tissue in vitro demonstrated a synergistic effect of down regulating expression of p-MEK1 and p-ERK1 when it was administered with erythromycin.